Mixing impeller device and method

ABSTRACT

An impeller assembly is mountable onto a rotatable shaft that has a flange extending radially from the shaft and rotating with the shaft. The impeller has at least one blade pair member having two opposed blades and central hub portion having a hole therethrough with an inner diameter at least as large as the outer diameter of the shaft, a plurality of corresponding mounting holes provided in each of the flange and the blade pairs, and a plurality of bolts for fastening the blade pair to the flange via the mounting hole.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a mixing impellerdevice and method. More particularly, the present invention relates toan impeller for mixing and blending materials such as gases, liquids andliquid suspensions.

BACKGROUND OF THE INVENTION

[0002] Mixing and blending applications, in particular the mixing andblending of liquids, liquid suspensions and gases, are often constrainedby the diameter of the tank in which the mixing is being carried out andby the diameter of the impeller. Some high solidity impeller designs (or“gas foils”) compensate for the aforementioned constraints by usingimpellers with three or four blades each having a large projected area.For example, it is known for existing high solidity impeller blades tooccupy 80% of their total swept area. In addition, some existingimpeller designs use impeller diameters which are typically 45% to 65%of the tank diameter. For a vessel of 240″ (20 feet) in diameter, theimpeller diameter is approximately 120″ (10 feet) in diameter dependingon service requirements, and the blades are approximately 60″ long andat least 38″ wide.

[0003] The impeller blades need to be inserted through a manway in thevessel for installation. In some covered mixing vessels, manways arecommonly 24″ in size and can pass impeller blades of up to 23″ in widthat best. Therefore, in order to insert larger blades, users either haveto install an oversized manway, (40″ in size for a 240″ diameter tank),or the blades must be supplied in a longitudinally split configurationand then assembled inside the vessel. Splitting the impeller blades isan expensive operation, especially for blades having a rounded, leadingedge, twist and curvature. In addition, multiple bolts are requiredalong with match marking to assure proper, gap free re-assembly. Thisprocess can be very difficult and time consuming because the inner andouter blade components must be aligned correctly so that the impellerbalance and blade geometry will not be compromised.

[0004] Further, some blades of known impeller design utilize a “blade toear” bolted connection for providing torque transmission, thrustreaction and blade support, in which the blades are each attached to anear extending from the shaft. The blades use symmetrical bolt patternsof 4, 5, 7 or more bolts to attach the blade to the ear of the hub. Thisconnection must be carefully designed, manufactured and assembled toassure problem free installation of the blades.

[0005] Also, known impeller designs usually provide 3 to 4 blades perimpeller. Thus, 12 to 28 bolts are required for blade attachment, andalloy bolts are often required. Alloy bolts are expensive and, dependingon the material, of limited availability. Many users require the use ofpositive locking of impeller bolts and hardware through the use oflocking plates, double nuts and/or safety wire, increasing the totalcost of each bolt. Due to the large quantity of bolts, it is usually notpractical for the end user to retighten the impeller hardware after theinitial period of operation, which can cause a loss of pre-load andpremature failure of the bolted connection.

[0006] Accordingly, it is desirable to provide a high solidity impellerfor mixing gas and liquid materials that offers improved reliability,reduced cost and ease of installation.

SUMMARY OF THE INVENTION

[0007] The present invention relates to impellers and impeller systemsfor mixing and blending applications. The invention is especiallysuitable for use in applications where the vessels are closed and arerelatively large in diameter.

[0008] In one aspect, the invention provides an impeller assembly thatis mountable onto a rotatable shaft that has a flange extending radiallyfrom the shaft and rotating with the shaft. At least one blade pairmember has two opposed blades and a central hub portion having a holetherethrough with an inner diameter at least as large as the outerdiameter of the shaft. A plurality of corresponding mounting holes isprovided in each of the flange and the blade pairs, and a plurality ofbolts for fastening the blade pair to the flange via the mounting holeis provided.

[0009] In another aspect of the invention, the impeller assembly furthercomprises at least one additional blade pair. The blade pairs arestacked onto one another, so that the blades extend radially at angularintervals to each other. The mounting holes align so that the boltsfasten all of the blade pairs to the flange.

[0010] In a third aspect of the invention, the flange has a frictionalfit key member and is releasably frictionally fit at a location alongthe length of the shaft.

[0011] In yet another aspect, the invention provides a method formounting an impeller assembly onto a rotatable shaft having a flangeradially extending from the shaft. The method comprises the steps ofinserting at least one member that has two opposed blades and a centralhub portion that has a hole therethrough with an inner diameter at leastas large the outer diameter of the shaft onto the shaft and into contactwith the flange. The method provides for fastening the blade pair memberto the flange so that it rotates with the shaft.

[0012] In a further aspect of the invention, the method additionallycomprises the step of fastening a second blade pair member having twoopposed blades and a central hub portion having a hole therethrough withan inner diameter at least as large as the outer diameter of the shaftonto the shaft in a stacked fashion onto the at least one blade pairmember.

[0013] There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

[0014] In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract included below, are for thepurpose of description and should not be regarded as limiting.

[0015] As such, those skilled in the art will appreciate that theconception upon which this disclosure is based may readily be utilizedas a basis for the designing of other structures, methods and systemsfor carrying out the several purposes of the present invention. It isimportant, therefore, that the claims be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a plan view of an eight bladed impeller using fourone-piece blade pairs in accordance with the present invention.

[0017]FIG. 2 is plan view of a one-piece blade pair having a driver dischub.

[0018]FIG. 3 is a side cutaway view of the impeller of FIG. 1 showingfour blade pairs mounted to a shaft.

[0019]FIG. 4 is a side view of an embodiment having a sliding fit hubwith an integral flange in accordance with the present invention.

[0020]FIG. 5 is a side view of an impeller in accordance with anembodiment where two shafts are attached by flanges.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0021] Referring now to the figures wherein like reference numeralsindicate like elements, FIGS. 1-5 illustrate presently preferredembodiments of an eight bladed gas foil impeller. While in theembodiment depicted the impeller is used for gas and/or liquid handlingin agitated vessels, it should be understood that the present inventionis not limited in its application to the blending and mixing of gasesand/or liquids.

[0022] Referring to FIGS. 1 and 2, there is shown a mixing impeller 10having four one-piece blade pairs 12 for a total of eight blades 14. Toform the blade pairs 12, individual blades 14 are welded directly to adrive hub 16, 180° apart. As seen in FIG. 3, each drive hub 16 bolts upin a stacked fashion to a rigid flange 18 which is welded to a shaft 20.This eliminates the normal blade-to-ear bolted connection of presentimpeller design and can thus provide improved torque transmission,thrust reaction and support of the blade weight through the attachmentof the stacked driver hubs 16 to the welded shaft flange 18.

[0023] The driver hubs 16 are attached to the welded shaft flange 18 byeight alloy bolts 21 through bolt holes 22 in the hubs 16. This boltattachment provides for angular indexing of the blades 14 to maintainproper tip-to-tip spacing and can simplify the field installation. Areduction in the number of bolts compared to ear designs is thuspossible and may be desirable due to the significant cost of alloybolts, their limited availability, and the fact that many applicationsrequire positive locking of the bolts by means of locking plates, doublenuts and/or safety wire.

[0024] In the embodiment of FIG. 3, the connection of the blades 14 tothe shaft 20 is via the one-piece blade pairs 12 where the driver hubs16 are stacked and bolted to the welded shaft flange 18. This connectionis not prone to fretting, corrosion, or seizing to the shaft 20 due tomaterial “pick-up.” This connection also is not dependent upon tighttolerancing to maintain performance. Therefore, the impeller 10 of thepresent invention can provide a more durable and more reliableshaft/blade connection than prior designs.

[0025] The aforementioned blade/shaft connection is also beneficialbecause the present design is based on a strength level equal to that ofthe shaft. Consequently it can offer improved reliability if theimpeller 10 is overloaded because the blades 14 deflect before theoverload forces damage the shaft 20. In addition, the connectionprovides for torque transmission primarily through friction betweenadjacent blade pairs 12 being compressed together and towards the flange18, rather than primarily through tensile loading/pre-load in bolts.This avoids a problem in some present impeller designs, where the boltswhich connect the blades to the shaft via an ear experience what isknown as load sharing where some bolts may experience significantlyhigher loads than others. This occurrence contributes to these presentimpellers having a propensity for selective bolt failure.

[0026] A benefit of the one-piece blade pair design 12 in combinationwith the welded shaft flange 18 design is that it uniformly distributesloads to all bolts 21, and using the one-piece design where two blades14 are incorporated, each blade 14 is subject to 50% of the load ispresent in four-blade designs.

[0027] Referring to FIG. 2, the blades 14 are shown connected to thedriver hub 16 to form the one-piece blade pairs 12. When installed, theblade pair 12 rotates about its central axis, for example, in thedirection A. Each of the blades 14 may be identical and formed in apress. The blades 14 have a tip 23 and a leading edge 24 and a trailingedge 26. An optional tip shape 25 is shown in dotted lines. When theblades 14 are installed, the tips 23 lie along the circumference of acircle defining the swept diameter of the impeller 10. The leading edge24 may be straight as shown in FIG. 2 or curved.

[0028] The blades 14 of the pairs are welded directly to the driver hub16, eliminating the need for many bolts and machined holes in impellershafts and blades. The blades 14 are air foils having camber and twistexcept at the hub end where they are attached to the driver hub 16.Upward and/or downward pumping is easily accomplished as a result of theblades 14 being welded to the driver hub 16. Accordingly, when theimpeller 10 rotated in a clockwise direction A, as shown, axial flow isproduced in the downward direction (downward pumping) in the liquid orliquid suspension in the mixing vessel. Alternatively, if the mixerdrive allows reversed rotation, the blades 14 can be selectivelyinstalled and the drive reversed to change the flow direction withoutrequiring additional or new parts.

[0029] Mixing impellers operate in an open flow field which leads toasymmetries in suction side velocities and direction. As shown in FIG.2, the present invention utilizes a blade 14 that is approximately only30% of the width of some presently known impeller blades. In addition,the increase in the blade number to eight (compared to having fewerblades), reduces the lift and drag on each blade, reducing the need forlarger shafts and larger drives.

[0030] The one-piece blade pair 12, as shown in FIG. 2, has a shapeintended to allow nesting with little material scrap. In a preferredembodiment, the blade 14 width is equal to 15% of the impeller 10diameter, enabling the one-piece blade pair 12 to easily fit through astandard manway. In addition, the driver hub diameter D is approximately18% to 20% of the total impeller diameter. For example, an impellerhaving a diameter of 120″ would have a driver hub diameter ofapproximately 22.8″. These dimensions enable the one-piece blade pair 12in this example to pass through the standard manway and be adequate toattach to flange designs up to 20″ pipe. Shafts of smaller diameter,particularly those suited for speed and shaft strength criteria,typically range from 5″ to 8″ in diameter, are also well suited foroperation with the one-piece design. Therefore, installation of theimpeller 10 is simplified due the impeller geometry. The blade pairs areeasily moved through standard manways without requiring the user tosplit the blades for entry through the manway and then reassemble theminside the mixing vessels.

[0031] The blade pairs 12 are easily shifted up the shaft due to aclearance between the inner diameter of the hole in the driver hub 16and the outer diameter of the shaft 20. Also, the one-piece blade pairdesign can be implemented using only eight bolts to attach the eightbladed assembly to the shaft via bolt holes 22.

[0032]FIG. 3 shows one preferred embodiment of the invention, andillustrates how the four blade pairs 12 are attached to the shaft 20. Inthe embodiment shown in FIG. 3, a shaft flange 18 is welded to the shaft20. The flange 18 may also be referred to as a driver disk. Bolts 21extend through respective aligned holes 22 in the flange 18, blade pairs14, and a clamp plate 30 to hold the blade pairs 13 so they rotatetogether with the flange 18 and the shaft 20. In this embodiment, eightbolts 21 are used to attach the blade pairs 14 to the hub 18. The clampplate 32 may be a single disk-shaped clamp plate, or may be a pluralityof individual clamp plates, one associated with each bolt 21.Alternatively, the clamp plate may be a suitable type of washer or maybe omitted entirely. If a clamp plate 32 is used, the clamp plate 32 canprovide for a uniform distribution of the bolt clamp load. Forapplications that require precision levels of balancing in either asingle plane (“static”) or in two planes (“dynamic”), an alignment pin(not shown) may be inserted through matching holes in the elements 18,14, and 32 for repeatability.

[0033] The flange 18 is usually machined in order to produce squarenessand concentricity to the shaft 20 centerline as well as achieving thenecessary flatness assuring a good bolted connection to the blade pairs12. The use of eight bolts 21 attaching the driver disk 18 to the bladepairs 12 provides for angular indexing of the blades to maintain propertip-to-tip spacing as well as simplifying field installation.

[0034]FIG. 4 illustrates another embodiment using a sliding fit hub 34that uses a hook key 36 that is tightened against the hub 34 to providea frictional fit against the shaft 20. The key 36 is a wedge-shapedelement and has an angled surface that mates against an angled surfaceinside the hub 34, and tightening of a bolt 38 that extends through thekey 36 and is threaded into the hub 34 urges the key 36 downwards, andhence radially inwards, to provide a tight frictional grip against thecircumference of the shaft 20. A lower ring 40 is bolted to the slidingfit hub 34 as shown via the bolts 21 to retain the blade pairs 12. Thesliding fit hub 34 arrangement permits the impellers to be mountedanywhere along the length of a shaft and permits, therefore, forvertical adjustment of the location of the impellers, as desired.

[0035]FIG. 5 illustrates another embodiment of the invention, whichprovides a combined shaft coupling and impeller attachment. In thisembodiment, an upper shaft 20 has a flange 44, and a lower shaft 42 hasa flange 46. Each of these flanges is welded at the end of itsrespective shaft. In the arrangement shown in FIG. 5, bolts 21 are usedextending through corresponding aligned holes 22 in the flange 44, theflange 46, the blade pairs 12, and a retaining clamp plate 32 to secureall these elements together so that they rotate together with the shafts20 and 42. In this way, the shafts 20 and 42 are connected to eachother, and the blade pairs 12 are also mounted at this location.

[0036] The above description and drawings are only illustrative ofpreferred embodiments which achieve the objects, features, andadvantages of the present invention, and is not intended that thepresent invention be limited thereto. Any modification of the presentinvention which comes within the spirit and scope of the followingclaims is considered to be part of the present invention.

What is claimed is:
 1. An impeller assembly mountable onto a rotatableshaft, comprising: a flange extending radially from the shaft androtating with the shaft; at least one blade pair member having twoopposed blades and central hub portion having a hole therethrough withan inner diameter at least as large as the outer diameter of the shaft;a plurality of corresponding mounting holes provided in each of theflange and the blade pairs; and a plurality of bolts for fastening theblade pair to the flange via the mounting holes.
 2. An impeller assemblyaccording to claim 1, further comprising at least one additional bladepair, wherein the blade pairs are stacked onto one another, so that theblades extend radially at angular intervals to each other, and where themounting holes align so that the bolts fasten all of the blade pairs tothe flange.
 3. An assembly according to claim 2, wherein the number ofblade pairs is four, thereby providing eight blade portions at equallyspaced angular intervals.
 4. An impeller assembly according to claim 2,further comprising a clamp member disposed on the opposite side of theblade pair from the flange, and wherein the bolts pass through theflange, the blade pair, and the clamp member to frictionally clamp theflange, the blade pair and the clamp member together.
 5. An impellerassembly according to claim 1, wherein the flange is welded to theshaft.
 6. A blade assembly according to claim 1, wherein the flange hasa frictional fit key member, and is releasably frictionally fit at alocation along the length of the shaft.
 7. An impeller assemblyaccording to claim 1, wherein the shaft is a first shaft and the flangeis located at the end of the first shaft, and the first flange isconnected by the bolts to a second flange that is located at the end ofa second shaft.
 8. An impeller assembly mountable onto a rotatableshaft, comprising: at least one blade pair member having two opposedblades and central hub portion having a hole therethrough with an innerdiameter at least as large as the outer diameter of the shaft; and meansfor fastening the blade pair to the shaft to rotate with the shaft. 9.An impeller assembly according to claim 8, further comprising at leastone additional blade pair, wherein the blade pairs are stacked onto oneanother, so that the blades extend radially at angular intervals to eachother, and wherein the fastening means fastens all of the blade pairs tothe flange.
 10. An assembly according to claim 9, wherein the number ofblade pairs is four, thereby providing eight blade portions at equallyspaced angular intervals.
 11. An impeller assembly according to claim 9,wherein the fastening means comprises a flange on the shaft, a clampmember disposed on the opposite side of the blade pair from the flange,and a plurality of bolts that pass through the flange, the blade pair,and the clamp member to frictionally clamp the flange, the blade pair,and the clamp member together.
 12. An impeller assembly according toclaim 11, wherein the flange is welded to the shaft.
 13. A bladeassembly according to claim 11, wherein the flange has a frictional fitkey member, and is releasably frictionally fit at a location along thelength of the shaft.
 14. An impeller assembly according to claim 1,wherein the flange is located at the end of a first shaft, and the firstflange is connected by the bolts to a second flange that is located atthe end of a second shaft.
 15. A method for mounting an impellerassembly onto a rotatable shaft having a flange radially extending fromthe shaft, the method comprising the steps of: inserting at least onemember having two opposed blades and a central hub portion having a holetherethrough with an inner diameter at least as large the outer diameterof the shaft onto the shaft and into contact with the flange; andfastening the blade pair member to the flange so that it rotates withthe shaft.
 16. A method according to claim 15, wherein the step offastening the blade pair member includes the step of bolting the bladepair member to the shaft with a plurality of bolts.
 17. A methodaccording to claim 15, further comprising the step of fastening a secondblade pair member having two opposed blades and a central hub portionhaving a hole therethrough with an inner diameter at least as large asthe outer diameter of the shaft onto the shaft in a stacked fashion ontothe at least one blade pair member.
 18. A method according to claim 17,wherein a number of blade pairs is four, and the four blade pairs arestacked onto one another and fastened to the flange.
 19. A methodaccording to claim 18, wherein the blade pairs are spaced at equalangular intervals.
 20. A method according to claim 15, wherein the stepof fastening the at least one blade pair member includes the step ofreleasably fastening the at least one blade pair member selectively at alocation along the length of the shaft via a frictional fit keyfastener.
 21. A method according to claim 15, wherein the shaft is afirst shaft and the flange is a first flange located at the end of thefirst shaft and wherein the fastening step includes the step ofcorrecting the first flange to a second flange that is located at theend of a second shaft.